In a known manner, pressurized water reactors comprise a reactor vessel filled with water under pressure in which the core of the reactor is contained, and also a primary circuit formed of several loops in communication with the reactor vessel. The primary circuit of a pressurized water reactor comprises, in a conventional manner, 3 or 4 loops connected in a symmetrical manner to the vessel of the reactor. FIG. 1 shows typically a loop of the primary circuit of a pressurized water reactor. Each loop of the primary circuit comprises:                a steam generator 1 in which the water under pressure cools, heating and vaporizing secondary feed water;        a primary pump 2, designated primary motor-driven pump or primary motor-driven pump unit (GMPP), ensuring the circulation of the water under pressure in the primary circuit.        
The primary circuit also comprises a pressurizer (not shown) connected to one of the loops by an expansion line.
Each loop of the primary circuit is formed by primary ducts comprising:                a hot branch 3 connecting the reactor vessel 6 to the steam generator 1,        a branch 5 having a U-shape, designated the U-branch, connecting the steam generator 1 to the primary motor-driven pump unit 2,        a cold branch 4 connecting the primary motor-driven pump 2 to the reactor vessel 6.        
The cooling water of the reactor under pressure is circulated in each loop by the primary motor-driven pump unit 2. The heated water in the reactor vessel 6, in contact with the core, arrives in the lower zone 1a of the steam generator 1, forming a water box, by the hot branch. The water then circulates in the tubes of the steam generator 1 where it cools, heating and vaporizing the secondary feed water. The cooled water then returns in the water box to be sent back to the primary motor-driven pump unit 2 by the U-branch 5, then to the reactor vessel 6 by the cold branch 4. The direction of circulation of the water under pressure is shown by way of indication by the arrows in FIG. 1.
The primary motor-driven pump unit 2 is a machine having a vertical axis, comprising in its upper part 2a an asynchronous electric motor fixed above a pump of the helico-centrifugal type, situated in the lower part 2b of the primary motor-driven pump unit 2, the electric motor and the pump being integrated by means of an element designated the motor stand 7.
The primary motor-driven pump unit 2 rests on articulated supports 9, typically three in number, having a swivel at each of their ends. The articulated supports 9 are disposed so as to permit the displacement of the primary motor-driven pump unit 2 under the effect of the thermal expansions of the primary ducts during the functioning of the reactor.
In a known manner, the primary motor-driven pump unit 2 is also held transversely by transverse holding devices (not shown).
The transverse holding devices, and also the articulated supports, permit slow displacements of the primary motor-driven pump unit within limits of permitted travel, i.e. typically slow displacements resulting from the expansion of the primary ducts.
In the case of rapid and consecutive displacements due to accidental situations, such as for example an earthquake or else a rupture of primary ducts, the transverse holding devices ensure the holding of the primary motor-driven pump unit transversely.
The transverse holding devices are disposed radially about the primary motor-driven pump unit along two concurrent directions generally forming an angle close to 90° and are connected to fixing means of the motor stand of the primary motor-driven pump unit.
In the known designs, the motor stand is a large-sized part made of steel, produced by foundry work.
The fixing means of such a stand are generally located at a height close to the placement plane of the fixing flange of the motor stand on which the motor is secured.
The fixing means are formed by a stirrup-shaped yoke produced during the production of the motor stand by foundry work and cooperate with the transverse holding device comprising a connecting arm. The connection between the yoke of the motor stand and the connecting arm of the transverse holding device is ensured by a transverse axis passing through the yoke and the arm so as to form a pivot link.
However, the manufacture by foundry work of the motor stand integrating the fixing means in the form of a yoke poses production problems owing to the large thicknesses required with respect to the fixing yokes.